/*
 * Copyright 2019 Web3 Labs Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
package org.web3j.utils;

import java.math.BigInteger;

import io.reactivex.BackpressureStrategy;
import io.reactivex.Flowable;

/** Flowable utility functions. */
public class Flowables {

	public static Flowable<BigInteger> range(final BigInteger startValue, final BigInteger endValue) {
		return range(startValue, endValue, true);
	}

	/**
	 * Simple {@link Flowable} implementation to emit a range of BigInteger values.
	 *
	 * @param startValue first value to emit in range
	 * @param endValue   final value to emit in range
	 * @param ascending  direction to iterate through range
	 * @return a {@link Flowable} instance to emit this range of values
	 */
	public static Flowable<BigInteger> range(final BigInteger startValue, final BigInteger endValue,
			final boolean ascending) {
		if (startValue.compareTo(BigInteger.ZERO) == -1) {
			throw new IllegalArgumentException("Negative start index cannot be used");
		} else if (startValue.compareTo(endValue) > 0) {
			throw new IllegalArgumentException("Negative start index cannot be greater then end index");
		}

		if (ascending) {
			return Flowable.create(subscriber -> {
				for (BigInteger i = startValue; i.compareTo(endValue) < 1
						&& !subscriber.isCancelled(); i = i.add(BigInteger.ONE)) {
					subscriber.onNext(i);
				}

				if (!subscriber.isCancelled()) {
					subscriber.onComplete();
				}
			}, BackpressureStrategy.BUFFER);
		} else {
			return Flowable.create(subscriber -> {
				for (BigInteger i = endValue; i.compareTo(startValue) > -1
						&& !subscriber.isCancelled(); i = i.subtract(BigInteger.ONE)) {
					subscriber.onNext(i);
				}

				if (!subscriber.isCancelled()) {
					subscriber.onComplete();
				}
			}, BackpressureStrategy.BUFFER);
		}
	}
}
